The present invention relates to a transforming system and a method of controlling the same and, more particularly, to a transforming system capable of satisfactorily protecting its components when a lightning stroke of large energy is exerted on transmission lines.
Generally, ground wires are laid along over head transmission lines to protect the overhead transmission lines from direct lightning strokes by carrying the current of a lightning discharge through a transmission line tower to the ground. However, it is difficult to completely prevent damage to overhead transmission lines from direct lightning strokes by the ground wires when direct lightning strikes occur. When a transmission line is struck directly by lightning, a lightning surge acts on the substation. Even if a direct lightning stroke on the substation is evaded, a lightning surge acts on the substation when the potential of the ground wire and the transmission line tower rises and a reverse flashover occurs. Since the overhead transmission line of a trunk line system, such as 500 kV, UHV overhead transmission lines, are laid in relatively hilly districts, sometimes horizontal lightning discharges occur and it is desired to protect aerial electric power lines from horizontal lightning discharges.
By establishing a lightning arrester in the substation, the overvoltage in the lightning stroke is suppressed.
However, when the energy of a lightning stroke exceeds the ability of the lightning arrester to suppress the over voltage, damage can occur. Further, once the lightning arrester loses the function of suppressing overvoltage, the substation protected by the lightning arrester can be damaged by a subsequent lightning stroke.
U.S. Pat. No. 5,532,897 and Japan Laid-Open 1981-71427 are prior art examples of protection systems using conventional lightning arrester.
The number of transmission line towers must be increased to protect overhead transmission lines from electric shocks, which, however, requires great expense. Ground wires cannot necessarily completely protect transmission lines from electric shocks even if the number of ground wires is increased.
And, means of protection of lightning arrester has not been shown in the Prior Art.
Accordingly, it is an object of the present invention to provide a transforming system and a method of controlling the same capable of satisfactorily protecting the equipment of a substation even if a transmission line is struck directly by an intense electric shock of a large energy, such as an electric shock of a waveform similar to that of a lightning stroke having a long duration (wave tail).
With the foregoing object in view, according to one aspect of the present invention, a power transforming system includes an overhead transmission line, and a transformer is connected with said overhead transmission line by the electric power line and a lightning arrester is connected with said electric power line, a grounding device is connected with said electric power line. When a lightning stroke is detected as arising in said overhead transmission line, a control device controls said ground fault device to make the ground fault condition whereby said grounding device protects said lightning arrester from said thunderbolt.
According to another aspect of the present invention, said grounding device is established between said overhead transmission line and said lightning arrester.
According to another aspect of the present invention, a circuit breaker is established between said overhead transmission line and said transformer, and said control device equipment cuts off said circuit breaker, after said ground fault device is operated.
According to another aspect of the present invention, a circuit breaker is established between said lightning arrester and said transformers, and said control device equipment cuts off said circuit breaker, after said ground fault device is operated.
According to another aspect of the present invention, said control device detects the thunderbolt by detecting the voltage and current state of said electric power line, and said control device provides an order signal for operating said grounding device.
According to another aspect of the present invention, said control device detects the thunderbolt by detecting the power frequency of said electric power line, and said control device provides an order signal for operating said grounding device.
According to another aspect of the present invention, a transformer connected with said overhead transmission line by the electric power line detects the thunderbolt by detecting the electric power condition of said aerial electric power line, and a ground fault condition is made in said electric power line after detecting that a thunderbolt arose in said aerial electric power line.